The commission previously has levied fines as high as $4.37 million against other cell phone firms for violating terms of city building permits. A commission rule requires cell phone companies to follow local laws intended to ensure that cellular transmission sites are built to protect public safety, architectural aesthetics and the environment.

T-Mobile spokesman Rod De La Rosa said the company's policy is "to work within all relevant and appropriate siting guidelines and regulations." T-Mobile had not been contacted by the commission, he said, adding that he was unaware of any failure to comply with the rules.

"If we receive details alleging otherwise, we would promptly investigate the matter and take any appropriate action," he said

Daniel Ceko, director of administration for Glotel, the Chicago-based technology firm that helped T-Mobile install the sites, said Glotel had not been contacted by the commission and declined to comment further.

The cell phone antennas and microwave dishes are typically less than 3-feet square, according to De La Rosa, who said that, depending on local rules, they are installed on commercial buildings, residences and water towers.

In rural areas, the firm may build larger cell phone towers, he said.

But two people familiar with the construction of cell transmission sites in Northern California told The Chronicle that T-Mobile supervisors were rushing to put the sites on air in order to earn bonuses, without complying with permit requirements.

One of them, who asked not to be named, said that in some cases, construction did not conform to the approved building plans.

"It happened every day," this person said.

Brian Lynch, a former Glotel employee, said, "I raised questions about these activities with Glotel. I mentioned that this was not the proper process ... and they fired me."

According to Lynch, T-Mobile retains Glotel to hire site construction managers. T-Mobile presses to build them quickly because T-Mobile supervisors receive quarterly bonuses based on the number of sites put "on air," he said.

T-Mobile's De La Rosa declined to comment on what he called "internal incentive metrics or other confidential business strategies."

The alleged violations have occurred in Marin, San Francisco, San Mateo and Santa Clara counties, the unnamed former employee said.